1. Field of the Invention
The present invention relates to a clamp nut which is mounted on a collet chuck body for holding tools in a collet, and which clamps the collet chuck body and the collet together. This invention also relates to a collet chuck including this clamp nut.
2. Description of the Related Art
A collet chuck has been used which is designed to hold a cutting tool by causing a collet to engage with a tapered hole in the top end of the chuck body provided on a machine tool and by using a clamp nut to clamp the cutting tool mounted on the collet, thereby causing the diameter of the collet to contract.
There is one type of such collet chuck in which a thrust ring and a nut body are integrated with each other so that the diameter of the clamp nut is made smaller in order to attain satisfactory balance. However, concerning the collet chuck having this configuration, heavy stress is exerted between the collet and the clamp nut, and seizure tends to occur. Accordingly, it is difficult to maintain tool-mounting accuracy.
Consequently, a collet chuck is suggested which prevents the occurrence of seizure by placing a thrust ball between a nut body and a thrust ring, which is placed between the nut body and a collet, thereby reducing a friction coefficient between the thrust ring and the nut body. Moreover, Japanese Utility Model Laid-Open (Kokai) Publication No. HEI 5-86407 discloses a collet chuck in which a low-friction mechanism is interposed between a front tapered part of a collet and a tapered surface of a clamp nut. Examples of this suggested low-friction mechanism include: a taper roller provided in a freely rotatable manner; a tapered disk with a low-friction surface; or the use of a low-friction material at least over a tapered surface of the clamp nut, a tapered disk, a taper roller, or the surface of a front tapered part of the collet.
However, concerning the collet chuck provided with the thrust ball or the taper roller as the low-friction mechanism, there is a possibility that balance would become worse due to deviation of an insertion opening position for the ball or the roller, or deviation of the ball or the roller placed in the collet chuck. Accordingly, there is a possibility that vibrations may tend to occur at the time of high-speed rotation. There is also the problem of high manufacturing costs.
Concerning the collet chuck provided with the low-friction mechanism by placing the tapered disk with the low-friction surface or by using the low-friction material at least over the tapered surface of the clamp nut, the tapered disk, the taper roller, or the surface of the front tapered part of the collet, low friction is suggested, but no consideration is given to the enhancement of lubricating property by constructing the above-mentioned parts by using a material with excellent lubricating property.